The present invention relates to a single-needle or multi-needle sewing machine, and more particularly to such a sewing machine having a sewing-material transport device.
German Patent 16 60 968 (equivalent to U.S. Pat. No. 3,495,558) discloses a sewing machine that has two upper transport wheels which are mounted for rotation on an extension fastened on an arm head of the sewing machine. The upper transport wheels are in engagement with two lower transport wheels which are mounted for rotation in a column which is arranged vertically on a machine base plate. On the top of this column there is provided a throat plate which has holes for the passage of two sewing needles, as well as suitable openings through which the upper portions of the lower transport wheels extend. The lower transport wheels, which are driven by the sewing machine, make it possible, in cooperation with the upper transport wheels, to advance the part being sewn during sewing. The sewing needles, which are inserted part of the time into the part being sewn, pull the part being sewn slightly upward near the point of insertion of the needle when they move upward, since there is no abutment above the throat plate to prevent the part being sewn from being carried along by the needles.
A further disadvantage of the known sewing machine resides in the fact that, at the end of the formation of a stitch, when the tightening of the thread takes place, the part being sewn is not held substantially motionless in the vertical direction between the throat plate and any abutment. Therefore, particularly when sewing thin material, fluttering can take place near the point of insertion of the sewing needle, so smooth pucker-free sewing is impossible.